Tank for draining a granular material/liquid mixture

ABSTRACT

A drainage tank for granular material/liquid mixture includes a low part and a high part provided with a lid. A device for separating the liquid and the granular material is arranged in the low part. A device for evacuating excess liquid is arranged in the high part and includes a number of overflow sleeves passing through the lid. The overflow sleeves have, above the lid, an overflow edge that is adjustable in height.

PRIOR ART

[0001] A granular material drainage tank is used in particular in a wetgranulation plant in which a molten product is introduced into apowerful stream of water which solidifies, granulates and cools it. Thisoperation is generally performed discontinuously in a granulating tankequipped for the injection of water of granulation. Once a batch ofmolten product has been poured into the granulation tank, and thereforegranulated, the granular material/water mixture is pumped from thegranulating tank to a drainage tank so that the granular material can beseparated from the water of granulation.

[0002] Such a drainage tank generally comprises a cylindrical upper partand a conical lower part which ends in an outlet portion equipped with ashut-off member. The conical lower part is also equipped, upstream ofthe shut-off member, with a device for separating the water and thegranular material, which comprises an annular collection chamber for thedrained-off liquid and filtering surfaces separating the inside of thereservoir from the annular collection chamber. The upper part is fittedwith a lid, fixed some distance from the upper edges of the upper part,so as to define a peripheral overflow slot. That represents a means ofremoving the excess liquid, to allow the excess water of granulation tobe evacuated. A channel is arranged around the drainage tank to collectthe overflowed water of granulation. The granular material/water mixtureis conveyed to the tank by means of a filling line that passes throughthe lid. When the drainage tank is filled, the granular material is heldback by the filtering surfaces, whereas the water is collected in thecollection chamber. The excess, or overflow, water can flow through themeans of evacuating excess liquid.

[0003] One disadvantage with such a drainage tank is that, depending onthe way in which the granular material spreads out within the tank,streams of water at higher speeds can form. These streams of water athigher speeds cause greater overflowing at certain points around theperiphery of the drainage tank, carrying with them fairly sizeableamounts of granular material. The overflowing of the excess water istherefore not uniform around the entire periphery of the drainage tank.In addition, the drainage tank is sometimes slightly inclined, and thisfurther accentuates this problem of non-uniform overflow.

PROBLEMS THAT THE INVENTION SETS OUT TO SOLVE

[0004] One problem underlying the present invention is that of proposinga tank for draining a granular material/liquid mixture which allows theexcess liquid to be removed more uniformly when the drainage tank isfilled. According to the invention, this objective is achieved by adrainage tank according to claim 1.

SUMMARY OF THE INVENTION

[0005] A tank for draining a granular material/liquid mixture accordingto the invention comprises a lower part and an upper part fitted with alid. A device for separating the liquid and the granular material isarranged in the lower part. A device for removing excess liquid isarranged in the upper part. According to an important aspect of theinvention, the device for removing excess liquid comprises a certainnumber of overflow sleeves passing through the lid. It will beappreciated that the overflow sleeves have, above the level of the lid,an overflow edge that is adjustable in height. The lid equipped with itsoverflow sleeves therefore constitutes an adjustable means of removingexcess water. This possibility of individually adjusting the height ofthe overflow edge of each sleeve allows the sleeves to be set up in sucha way as to obtain essentially equivalent overflows of liquid througheach of them, thus ensuring uniform overflow. In general, to obtainuniform overflow, the overflow edges of the sleeves will preferably beadjusted so that they lie in one and the same horizontal plane. It willalso be noted that the overflow sleeves make it possible to compensatefor any inclination of the tank. A drainage tank according to theinvention is particularly well suited to the drainage of a granularmaterial/water mixture pumped from a granulating tank.

[0006] According to a preferred embodiment, an overflow sleeve comprisesa vertical pipe welded, advantageously in a sealed manner, into the lidand equipped with a threaded upper end above the level of the lid. Athreaded adjustment ring is screwed onto the threaded upper end of thevertical pipe. This threaded adjustment ring forms the overflow edge,and can therefore be adjusted along a vertical axis, so as to set theoverflow height.

[0007] The overflow sleeves are advantageously distributed uniformlyover the lid. The excess liquid therefore overflows at various pointsacross the cross section of the drainage tank, rather than just at itsperiphery. This makes it possible to have essentially equal liquidspeeds inside the drainage tank, across its entire cross section. Theoverflow speeds will therefore generally be lower, thus making forbetter deposition of the granular material and avoiding the entrainmentof particles. Such a distribution of the sleeves contributes to uniformoverflowing of the excess liquid. In order to obtain essentiallyequivalent liquid speeds across the entire cross section of the tank, itis possible, for example, to distribute the sleeves in such a way thatthey are assigned to the removal of liquid from regions of the lid thathave identical surface areas.

[0008] One parameter on which the overflow depends is the total lengthof the overflow edges offered by the sleeves. In order to guaranteeappropriate removal of the liquid, care will preferably be taken toensure a total overflow length at least equal to that of a conventionaltank with a peripheral slot. This condition entrains that the number ofsleeves in the lid preferably be such that the sum of the lengths of theoverflow edges of the sleeves be no shorter than the external perimeterof the drainage tank.

[0009] The lid advantageously has an essentially convex shape, e.g.conical shape, so that the liquid which has overflowed through theoverflow sleeves runs toward the periphery of the lid. The liquid whichhas overflowed can be collected in a liquid-collecting channel runningaround the lid.

[0010] The device for separating the liquid and the granular materialpreferably comprises an annular collection chamber for the drained-offliquid and filtering surfaces separating the inside of the drainage tankfrom the annular collection chamber. In general, the lower part ends inan outlet portion in which a shut-off member is mounted. During thefilling of the tank, the shut-off member is closed. The granularmaterial is held by the filtering surfaces and is deposited in thedrainage tank while the liquid flows through the filter surfaces and isremoved via the collection chamber. The excess liquid runs though theoverflow sleeves. Once the water has flowed out of the tank, theshut-off member is opened and the drained granular material isrecovered, for example on a conveyor belt passing under the outletportion or into a vat.

[0011] Once the liquid has flowed out of the drainage tank, therenonetheless remains a certain amount of water in the outlet portion,just above the shut-off member. In order to remove this residual waterbefore opening the shut-off member, the outlet portion is advantageouslyequipped, just before the shut-off member, with a secondary separatingdevice. It comprises filtering surfaces separating the inside of theoutlet portion from a secondary annular collection chamber. The residualwater from the outlet portion can therefore be removed via thissecondary separation device.

[0012] The granular material/liquid mixture is preferably conveyed intothe drainage tank by means of a filling line passing through the lid insuch a way as to be coaxial with a vertical central axis of the drainagetank.

[0013] Advantageously a deflector forming an impact surface is installedbelow a mouth of the filling line, so that the granular material/liquidmixture leaving the filling line strikes the impact surface of thedeflector. The impact surface of the deflector may for example beessentially flat or conical. The particles of granular material aretherefore slowed as they hit the impact surface of the deflector, andthis prevents the finer particles among them from being carried along byascending liquid streams. In order to improve the flow of thewater/granular material mixture in the tank still further, this tank isadvantageously equipped with a filling chamber stretching verticallyfrom the lid and open toward the bottom. The filling chamber surroundsthe mouth of the filling line and the deflector. The cross section ofthe filling chamber is such that there is a passage between this chamberand the deflector for the mixture to leave. Such a structure makes itpossible to limit the turbulence in the drainage tank while it is beingfilled, and plays a part in a uniform overflowing of the excess liquid.Still in order to limit turbulence in the drainage tank, the drainagetank advantageously comprises a guide chamber stretching vertically fromthe lid and open toward the bottom. The guide chamber surrounds thefilling chamber and has a larger cross section than the filling chamber.

[0014] The overflow sleeves may be fitted with retention filters, so asto retain particles which get as far as the sleeves.

DESCRIPTION WITH TH AID F TH FIGURES

[0015] Other particulars and features of the invention will becomeapparent from the detailed description of one advantageous embodimentset out hereinbelow, by way of illustration, and with reference to theappended drawings. These show:

[0016]FIG. 1: a front view of a preferred embodiment of a drainage tankaccording to the invention, the part above the broken chain line beingshown in section;

[0017]FIG. 2: an enlarged view of detail A of FIG. 1;

[0018]FIG. 3: a view from above of the tank of FIG. 1, without thefilling line; and

[0019]FIG. 4: a view in vertical section of an outlet portion equippedwith a secondary separating device.

[0020]FIG. 1 illustrates a preferred embodiment of a drainage tank 10 inaccordance with the invention. The drainage tank 10 comprises a lowerpart 12 of conical shape, supported in a framework 14, and a cylindricalupper part 16 surmounting the bottom part 12. The upper part 16 isequipped with a lid 18 covering the top of the drainage tank 10. The lid18 has, passing through it, a filling line 20 which is used to fill thedrainage tank 10 with a granular material/liquid mixture that is to bedrained. This filling line 20 passes through the lid 18 in such a way asto be coaxial with a vertical central axis 22 of the drainage tank 10.The bottom part 12 ends in an outlet portion 24 equipped with a shut-offmember 26. In the bottom part 12, upstream of the outlet portion 24,there is a device for separating the liquid and the granular material,generally labeled 28. The separating device 28 comprises an annularcollection chamber 30 for the drained-off liquid and filtering surfaces31 (shown as hidden detail in FIG. 1), separating the inside of thedrainage tank 10 from the annular collection chamber 30. The referencesymbol 32 indicates a discharge line for the drained-off liquid to leavethe annular collection chamber 30. A valve 33 is preferably mounted inthis discharge line 32.

[0021] It will be appreciated that the lid 18 has, passing through it, acertain number of overflow sleeves 34 which, above the level of the lid18, have an overflow edge the height of which can be adjusted. Theseoverflow sleeves 34 represent a device for removing excess liquid, withan adjustable overflow height. What these actually do is allow theremoval of the excess liquid during the filling of the drainage tank 10.Typically, when filling the drainage tank 10, the shut-off member 26 isclosed and the tank 10 is filled with the granular material/liquidmixture conveyed via the filling line 20. The granular material isretained by the filtering surfaces 31 and accumulates in the tank 10whereas the liquid flows through the filtering surfaces 31 to then beremoved by the collection chamber 30. When the tank 10 is filled withmixture up to the height of the lid 18, and the tank 10 continues to befilled, the excess liquid flows out through the overflow sleeves 34. Itwill be noted that, as the tank 10 is filled, the valve 33 isadvantageously kept shut until the level of granular material in thebottom part 12 of the tank 10 is above the filtering surfaces 31. Oncethis level of granular material has been reached, the valve 33 is openedand the liquid is filtered through the deposited granular material thenthrough the filtering surfaces 31 before entering the annular collectionchamber 30. By adopting this procedure, the granular material is used asan additional filtering means, and the filtering of the liquid in thedrainage tank 10 is more effective.

[0022] As can best be seen in FIG. 2, an overflow sleeve 34 comprises avertical pipe 36 which is welded in a sealed manner into the lid 18 andwhich has a threaded upper end above the level of the lid 18. Screwedonto this threaded upper end is a threaded adjustment ring 38, whichforms the overflow edge of the overflow sleeve 34. The overflow sleeves34 are therefore individually adjustable. To guarantee uniformoverflowing of the excess liquid through all the overflow sleeves 34,their overflow edges are generally set so that they lie in one and thesame horizontal plane. It will be noted that this possibility ofindividual adjustment in particular makes it possible to compensate forany inclination of the drainage tank 10. In addition, the overflowsleeves 34 are preferably distributed uniformly across the lid 18, asshown in FIG. 3, so that they are assigned to the removal of liquid fromregions of the lid 18 which have identical surface areas. That makes itpossible to have essentially equal liquid speeds across the entire crosssection of the tank 10. It will also be noted that, in this preferredembodiment, it is desirable for the overflow length offered by thesleeves 34 not to be shorter than the overflow length offered by aconventional drainage tank with a peripheral slot, that is to say itsperimeter. For example, if the diameter of each sleeve 34 is denoted Dm,the diameter of the tank 10 is denoted Dr, and the number of sleeves 34is denoted Xm, then the abovementioned condition translates asXm×(Dm×π)≧(Dr×π). The number of sleeves Xm must therefore preferably begreater than the ratio Dr/Dm.

[0023] In FIG. 1, it can be seen that the lid 18 has a conical shape,which means that the liquid which has overflowed through the sleeves 34runs toward the periphery of the lid 18. A collecting channel, indicatedby the reference symbol 40 in FIGS. 1 and 3, runs around the lid 18 tocollect the liquid running off the lid 18.

[0024] In FIG. 1, the reference symbol 42 indicates a disk-shapeddeflector fixed under the mouth 44 of the filling line 20. Thisdeflector 42 is centered with respect to the central axis 22 of the tank10 and forms a roughly horizontal impact surface. It will be noted thatthe mouth 44 of the filling line 20 and the deflector 42 lie inside acylindrical filling chamber 46 stretching vertically from the lid 18 andopen downward. The deflector 42 is fixed to the walls of the fillingchamber 46. The cross section of the filling chamber 46 is such thatthere is an annular space 48 between the deflector 42 and the fillingchamber 46 for the passage of the mixture. The mixture conveyed by thefilling line 20 therefore first of all enters the chamber 46 and strikesthe impact surface, on which it is slowed, then leaves the chamber 46via the annular space 48. The use of the deflector 42 at the entry tothe tank 10, supplemented by the chamber 46, makes it possible to limitturbulence inside the tank 10.

[0025] In order to limit still further the turbulence inside the tank10, a cylindrical guide chamber 50 is provided, this stretchingvertically and being open downward. The guide chamber 50 surrounds thefilling chamber 46 and is fixed some distance from the lid 18, so thatat the top of the guide chamber 50 there is an annular slot 52 for thepassage of the liquid. The cross section of the guide chamber 50 isgreater than that of the filling chamber 52.

[0026] Once filling is complete and the liquid has flowed out of thetank 10 via the separating device 28, some liquid generally remains inthe outlet portion 24 between the bottom of the separating device 28 andthe shut-off member 26. If this residual liquid is not removed, it flowsout with the drained granular material when the shut-off member 26 isopened. To overcome this problem, a secondary separating device may bemounted at the outlet portion 24. This is illustrated in FIG. 4, wherean outlet portion 24′, similar to the one in FIG. 1, is equipped with asecondary separating device generally indicated 54. The outlet portion24′ is equipped with an upper flange 56 for connecting it to theseparating device 28 and with a lower flange 58 for connecting it to theshut-off member 26. The secondary separating device 54 comprisesessentially annular filtering surfaces 60 which separate the inside ofthe outlet portion 24′ for a secondary annular collection chamber 62.The liquid lying in the outlet portion 24′ can therefore flow throughthe filtering surfaces 60 and the granular material is retained insidethe outlet portion 24′. The reference symbols 64 and 64′ indicate twosecondary discharge lines for the liquid to leave the secondarycollecting chamber. The secondary discharge lines 64 and 64′ areadvantageously each fitted with a secondary valve (not shown), whichvalves would preferably be operated like the valve 33 of the separatingdevice 28.

1. A tank for draining a granular material/liquid mixture comprising: alower part (12) and an upper part (16) fitted with a lid (18); a device(28) for separating the liquid and the granular material and arranged insaid lower part (12); a device for removing excess liquid and arrangedin said upper part (16); characterized in that said device for removingexcess liquid comprises a certain number of overflow sleeves (34)passing through said lid (18), said overflow sleeves (34) having, abovethe level of said lid (18), an overflow edge that is adjustable inheight.
 2. The drainage tank as claimed in claim 1, characterized inthat such an overflow sleeve (34) comprises: a vertical pipe (36) weldedinto said lid (18), said vertical pipe (36) having a threaded upper endabove the level of said lid; and a threaded adjustment ring (38) whichis screwed onto said threaded upper end of said vertical pipe (36), saidthreaded adjustment ring (38) forming said overflow edge.
 3. Thedrainage tank as claimed in claim 1 or 2, characterized in that saidoverflow sleeves (34) are distributed uniformly over said lid (18). 4.The drainage tank as claimed in any one of the preceding claims,characterized in that the number of sleeves (34) with which the lid (18)is equipped is chosen so that the sum of the lengths of the overflowedges of the sleeves (34) is no shorter than the perimeter of the upperpart (12) of the drainage tank (10).
 5. The drainage tank as claimed inany one of the preceding claims, characterized in that said lid (18) hasan essentially convex shape so that the liquid which has overflowedthrough said overflow sleeves (34) runs toward the periphery of said lid(18).
 6. The drainage tank as claimed in any one of the precedingclaims, characterized by a liquid-collecting channel (40) running aroundsaid lid (18).
 7. The drainage tank as claimed in any one of thepreceding claims, characterized in that said device (28) for separatingthe liquid and the granular material comprises an annular collectionchamber (30) for the drained-off liquid and filtering surfaces (31)separating the inside of said drainage tank (10) from said annularcollection chamber (30).
 8. The drainage tank as claimed in any one ofthe preceding claims, characterized by an outlet portion (24′) endingsaid lower part (12) of said drainage tank (10), in which a shut-offmember (26) is mounted; and by a secondary separating device (54)mounted in said outlet portion (24′) upstream of said shut-off member(26), said secondary separating device (54) comprising filteringsurfaces (60) separating the inside of the outlet portion (24′) from asecondary annular collection chamber (62).
 9. The drainage tank asclaimed in any one of the preceding claims, characterized by a fillingline (20) of said drainage tank (10), which passes through said lid (18)in such a way as to be coaxial with a vertical central axis (22) of saiddrainage tank (10).
 10. The drainage tank as claimed in the precedingclaim, characterized by a deflector (42) forming an impact surface belowa mouth (44) of said filling line (20), so that the granularmaterial/liquid mixture leaving said filling line (20) strikes saidimpact surface of said deflector (42).
 11. The drainage tank as claimedin the preceding claim, characterized by a filling chamber (46)stretching vertically from said lid (18) and open toward the bottom,said filling chamber (46) surrounding said mouth (44) of said fillingline (20) and said deflector (42), and the cross section of said fillingchamber (46) being such that there is a space between this chamber andsaid deflector (42).
 12. The drainage tank as claimed in the precedingclaim, characterized by a guide chamber (50) stretching vertically fromsaid lid (18) and open toward the bottom, said guide chamber (50)surrounding said filling chamber (46) and having a larger cross sectionthan said filling chamber (46).
 13. The drainage tank as claimed in anyone of the preceding claims, characterized by a retention filter in theoverflow sleeves (34).
 14. The use of the drainage tank (10) as claimedin any one of the preceding claims for draining a batch of granularmaterial/water mixture pumped from a granulating tank to said drainagetank (10).